I have two 36" sink base cabinets on either side of an 18" drawer base.

I have an 93" vanity. It is custom made but you could probably duplicate most or all of the setup with something stock. We have two 24" bases, a 15" center base with drawers (one tall drawer and three short ones) and a 15" base on either end with one small drawer and a hamper underneath (so we have two hampers--one for darks and one for whites). So it's 15-24-15-24-15.

Thank you so much. Do they blend together pretty well? I want to do stock but haven't seen a lot of 2-3 piece selection. Now how do you go about getting a counter top with sink cut outs. I told you.... I am new to this!! LOL
Do you have any pictures?

You get the top made separately. A single top, with holes for the sinks and faucets. That is, if you are mounting the faucets on the top and not on the wall.
I got Adelphi cabinets, who make their stock cabinets to the inch.

If you google "RTA cabinets" you will find a number of sites selling vanity cabinets that you can put together in numerous configurations to end up being 90". As far as the top, you pick the material you want, i.e. granite, marble, etc and have the fabricator cut it, edge it and cut out the sink and faucet holes. We have a 93" vanity two 34" sink cabinets with a 25" vanity in the middle. We were going to replace it with RTA cabinets, but I refinished it and am putting a shelf in the vanity space, will use the top half for towels and put a hamper under the shelf.